Nope, you need them both...

I would go for both. In fact, I did. If you only use cold water, you could go for the single. Might be hard washing greasy dishes, though. :-)
Lisa

I'm not understanding the question and answers entirely, so I'll just try to describe:

There are two valve gizmos in the Tapmaster that go on the water lines that feed your sink. The foot controller uses air pressure in tubes to operate them. The hot and cold both go on when you press open and both close when you release. They both lock open when you set the lock, and both close when you release it. That's all it does.

So to make it operate the water, you set the mixer or taps at the flow rate and temperature you like best and leave them on. Use the Tapmaster to turn them off, and then turn them on again. If you want to turn off the Tapmaster, for instance when relatives come to stay, or you're changing temperatures a lot, you lock open the Tapmaster and use the mixer/taps to turn the water on and off. If you're using the Tapmaster you adjust the temperature and flow with the mixer/taps as normal. Just don't turn them off.

Does that make sense?

If you want a separate Tapmaster for the hot and the cold you could probably make it work, but since you can't adjust the quantity with the foot controller I can't see the point of doing that.

If I remember correctly, in addition to the single foot pedal model plllog described, there is another model that allows you to control the hot and cold separately. It is significantly more expensive. Most Tapmaster owners on this forum (including myself) have the single foot pedal model and are happy with it.

Do you turn or leave the controls of the faucet on? My son has a pre wash faucet. He leaves the control on all the time and when he wants to use it, just presses the thingy on the sprayer.